You’re just trying to get the device into a known good state.
The truth is that it’s rarely worth trying to find the root cause of an issue unless it’s a frequent problem.
Something somewhere went wrong. We don’t know if it’s a hardware or software issue, so we’ll try a solution that covers both.
Powering the device off stops the flow of electricity, and waiting a few seconds makes sure that any capacitors (think of very tiny, very fast batteries) bleed off the power they’ve stored. Then turning it back on makes it go through the full startup process which is likely to result in a working state.